1. Field of the Invention
The present invention relates to a system and method for controlling a function, such as a vehicle function, using a variable sensitivity receiver.
2. Background Art
It is known in the automotive industry to provide for remote control of a vehicle function, such as through the use of remote keyless entry (RKE) systems. Such RKE systems typically use a hand-held remote transmitter (i.e., transponder), which is commonly referred to as a “fob” or “card.” Currently available RKE fobs may be separate units, or may be part of an ignition key head. Such RKE fobs generally transmit radio frequency (RF) signals to a vehicle transponder in order to lock or unlock vehicle doors, open or close a vehicle sliding door, unlock a vehicle trunk, activate internal and/or external vehicle lights, activate a “panic” alarm, and/or perform a variety of other functions.
RKE systems may be characterized as active or passive systems. In active RKE systems, a switch or pushbutton on the remote transmitter must be activated by an operator in order to have a desired remote access function performed, such as locking or unlocking the vehicle doors. In passive RKE systems, however, no such switch or pushbutton activation by an operator is required in order to perform a desired remote access function.
More specifically, in a passive RKE system, a remote transponder, which again may be referred to as a “fob” or a “card,” is typically provided for communicating with a transponder and/or control unit (i.e., receiver) installed in the vehicle. The vehicle transponder and/or control unit is provided in communication with door locking mechanisms to lock and unlock the vehicle doors in response to lock or unlock signals received from the remote transponder. In that regard, the remote transponder is carried by an operator and is designed to automatically unlock the vehicle as the operator approaches the vehicle, without the need for operation of any switch or pushbutton by the operator. Similarly, the system is further designed to automatically lock the vehicle as the operator, carrying the remote transponder, moves away from the vehicle.
It is further known in the automotive industry that a distance between a fob and a vehicle transponder may be determined by calculating the strength (i.e., power, watts) of a fob generated signal at the vehicle transponder. Such vehicle remote keyless entry systems generally use the distance to determine whether to perform a requested function. However, such vehicle remote keyless entry systems generally require a controller capable of calculating the power of a received signal. In that regard, a system and method for controlling a function that avoids the complexities associated with determining the power of a signal may be desirable.